Petroleum pitch and process for its manufacture



Aug. 12, 1958 BEUTHER ET AL 2,847,359

PETROLEUM FITCH AND PROCESS FOR ITS MNUFACTURE Filed July 2, 1953 ONT u United States Patent PETROLEUM PITCH AND PROCESS FOR ITS Hroldf'BeItlieQ-P'l1n Township, Allegheny County, and Willam"C. Difutt and .Patil'Sieckeg Munt Lebanon Township). Alle'ghny'Cou-ilty, P.; assgn'or's, b'y'dire'ct andmesie assignments, to Gulf-Research & Development'Colanyg-Pittsburgh, Pa., a'cbrporationof Delaware @puentenet-'n z, 1953; sensi No. 365,644 sfclaims. (el. 19t- 50) invention.relates` to petroleum pitches,van'd more particularlyto petroleum pitches having very high softening points, and l"a process for their preparation.

Crude petroleum oil as received at thelrenery is processed into marketable products which differ in kmany of theirpr'operties and` uses, but are separated from one another principally byL their different boiling ranges. Usually, the more volatile, distillate products, namely gasoline, kefrbsene',.disel fuel, and domestic heating oil, may be sold'atfrelativelyhigh prices and,thus, bring the highe'streturn on ythecrucle oil. The market price of heavy residual fuel oils, commonly identified as No. 6 fiiel'orilv, is vmuch lower than the price of the distillates, and/generally. is even lower than the price yofthe crude oil. Moreover, in order for` the No. 6 fueloil to meet theusal specifications, particularly in regard to viscosity, it' is necessary to blend the residualproducts with a light oil of lowviscosity, commonly a cycle oil from `catalytic or"thcrnia1"cra'cking operation, usually referred to as a cutteroilf- 'Hius, catalytic cycle'oil used asa cutter is degradedfroml a product of relatively'high value, such as a domestic heating oil, to theloW-priced No. 6 fuel oil.

l Several refining techniques have been employed in an elfo'r't to reducel the amount of No. 6` fuel oil obtained from Vcrude oil. A commonly usedprocessis to subject the'residal'oil obtained Y'from the atmospheric distillation of th'e'cr-ud'e lt'o a mild cracking operation known as visbr'eaking. The viscosity of the residual loil is reduced by l the visbreaking which also provides small amounts of cia'cked'dis'tillates. The, degree of cracking in the usual visbrakingprocess islmited'b'y' the serious coke formation of lresidual stocks `c'onta'ininghea'v'y oils when severe- 1y cracked.

Ailthifrproce'ss which rhas been used to reduce the amountof No. 6 fueloil is the vacuum distillation of the crlidefo'il to form ,a relatively small amount of a very heavyY virgin residue. The virgin residue is ythen blended with a cycle oilto-a specification viscosity. While,l `l`thisl` process.- does't'iprovide added; `quantities" of a distillate which= may: be`usedas' a f cracking f charge stock, the amount'ofcutter oil required VtoY blend with the `heavy vresidue'nis relatively large.

A'prbce'ss `inl which the production of a No. 6 fuel oil is completely eliminated is a coking operation. In that process, the residual product from the initial distillation of the fcrude is cracked in a drum or chamber under longperiod, low-severity operating conditions to form` a crackeidfdisrtil teand coke.- The coking-operation'is an I s rin" which lc'on'sderable diiculty and high labor and utility costs are encountered in removing the coke from the drums in which it is formed and collected. f

. Iny our; application Serial No. 262,566, entitled ThermalConversion ofRcducedaCrudes, filed December 20,

1951snow; U; S. -Patent No. 2,762.754, a process is describediandficlaimed' inf-Which -a--crude oil -is subjected 'to -a`V very de epyfvacuum reduction to producel a virgin ,2. residual stockhaving an-initial boiling point generally inthe range of 900 and '950 F. The residual stocks have-a Conradsoncarbonresidue number-'of at least `18, an API `gravity of below 10,7V and a viscosity, SUS at 210 F. of at least 6000. It has beenl found that a residual stock of thatv'typemay be visbroken at unexpectedly high severities ,fory short periods without excessive coke formation. While the more severe visbreaking conditions made possible by. the extremely deep vacuumreduction ofthe crudeI markedly reduce the amount and the viscosity of the bottomsfrom the visbreaking opera.- tion, it is stillA necessary to blend someA relatively highpriced catalytic cycle stock with the bottoms toproduce a No. 6 fuel oil having anacceptable"viscosity,

Accordi-ng to this invention,.the value o f the products from certain crude petroleum oils is markedly increased lby the preparation of a novel, high-softening point petroleum pitch in'place of` the No. 6'fuel oil. The pitch is prepared by a deep vacuum reduction of a parafiinic or mixed base crude oil followed by the visbreaking of the bottoms thus producedl at conditions of high severity. The visbroken material is then Isubjectedto a second vacuum distillationv at'ext'remely high distillation temperatures, such-as approximately 1100 P. (corrected to 760 millimeters of mercury) to produce a high-softening p'oint petroleum pitch asaY residue.

'I'hesingle'figr Vofthe drawngsis a diagrammatic flow Sheet `ofa1J'i'c3`tz'cs'sfip'oducing, the petroleum pitch of thisL invention.

The no'vel petroleum pitches ofA this invention are characterized by a very high softening point, as determinedbytheringfaii tifall'A. S. test No. D-36-26, above about" 350T F; In most' instances the softening point will'fall within the r'alnge' of `350 F. to 450 F. TheY softening point will 'depend upon' the' characteristics ofy the charge stock' as well as' the' severity of the visbreaking conditions andA the distillation temperature employed in theV` ldistillationl following the visbreaking. Increasing the severity of the visbr'eaking and increasing the temperature oftheeln'al vacuum distillation each tend to increase the softening temperature of the pitch. Pitches having softening points above 450 F. may readily be 'prepared by a suitable selection of charge stock and visbreakingf and distillation temperatures. Throughout the specification' and claims of this application the term softening p'oin of a pitch shall refer to' thesoftening point a's determined by A. S. T. M". test No. D-36-26 and the term distillation temperature shall mean ldistillation temperature' corrected to a pressure ofV 760 mm. of Hg,absolute', u'nle'ss- Iotherwise indicated. Y

Ther pitches may' be' liquefied' a't temperatures of 650 F. to 750 F. andlcast in` any desired shape. The petroleum pitches have a low penetration and are brittle. Their penetration, which is of the' order of 0 to 5 as determinedfinaccordan'ce withA. S. T. M. test No. D-5-49 at-210 F., 100 grams,- and 517se`c'onds, has a low Variatio'n'with changes in temperature, as indicated by a su'sceptibility factor generally ranging-from about 15 to 25.

Chemically, the petroleum pitchesare unlike coal tar pitchesror petrolt'e'um. coke. The pitches are practically completely soluble in benzene, oar-bon disulfide or trichloroethylene, which indicates the absence of free carbon or coke-like constituents. For example, the solubility'of the pitches in` trichloro'ethylene is of the order of 99-ll%'. However, the Conrad'son carbon residue of the pitches, as determined by A. S. T. M'. test No. D-l89-46 is above about 40%. The. tar-insoluble material, as measured by dissolving in a refined grade of creosote (Kolineum), is less than about 0.4%. The acetone-'insoluble material'in-the petroleum pitches varies within the range ofV approximately.- to. 95%;

The properties of the petroleum pitches are such that they may be used as a substitute for gilsonite in the compounding of paints and rubber. They have low speciiic gravities, generally below about 1.200, for example from about 1.050 to 1.200, but' preferably from 1.100 to 1.200, probably resulting from the absence of synthetic asphalt formation in their preparation. The definite softening point and the possibility of liquefying the petroleum pitches allows their use as a binder. The ybrittleness of the pitches allows them to be readily ground and used as a powdered fuel.

The process for. the preparation of petroleum pitches according to this application is particularly suitable for use on paraflinic and mixed base crude oils. Typical crude oils which may be successfully and economically treated according to this invention are those from Kuwait, Mid-Continent and West Texas fields. High softening point petroleum pitches may also be prepared from more naphthenic crudes by the process herein described but those crudes may also be processed by a more simple, economical and direct process to prepare solid petroleum pitches.

Referring to the single figure of the drawings in which a flow sheet of the process used in the preparation of the petroleum pitches is illustrated diagrammatically, a crude oil is introduced through line into an atmospheric distillation tower 12. The crude oil is heated in any conventional manner prior to introduction into the atmospheric tower 12 to supply the heat necessary for the vaporization of the volatile fractions. Gas is taken from the top of the tower through a line 14 and the usual side streams such as one of gasoline, naphtha, and a heavy fraction, for example a 400 to 650 F. fraction, may be removed as side streams through lines 16, 18, and 20, respectively. The atmospheric distillation tower 12 and its operation are conventional and clearly other arrangements of lfractionating equipment for the separation of the various fractions may be made without vdeparting from this invention. l

The bottoms from atmospheric tower 12 are withdrawn through a line 22 and delivered to a heater 24. The heater 24 heats the bottoms suiciently to allow a very deep vacuum reduction of the bottoms in the vacuum tower 26. The upper temperature limit to which the bottoms from the atmospheric tower may be heated in heater 24 will depend upon the maximum temperature which may be employed without excessive thermal conversion of the bottoms. The temperature of the bottoms discharged from the heater 24 will generally be from 700 F. to 800 F.

The hot bottoms are delivered from heater 24 through line 28 into the vacuum tower 26 in which a very deep cut is made to form a heavy residue. Theconditions of vacuum and temperature in the vacuum tower are such that a distillation temperature, corrected toa pressure of 760 mm. of Hg, of approximately 1000`F. is obtained. A heavy gas oil, suitable as a catalytic cracking charge stock, is removed from the top of vacuum tower 26 through a line 30. The residue from the vacuum tower is taken therefrom through line 32 at the bottom of the tower 26 and delivered by means of a pump 34 to a visbreaking furnace 36. v

The vacuum distillation in tower 26 is such that the residue from the vacuum tower 24 will have an initial boiling point of approximately 900 to 950 F., a Conradson carbon residue in excess of 18, a gravity less than 10 API, and an SUS viscosity at 210 F. greater than 6,000. In highly paraflinic crudes, the residue from the vacuum tower 26 may be as low as 5 percent of the total volume of the crude. In other crude oils which may be processed according to this invention to produce the novel petroleum pitches, such as a Kuwait crude, the residue from the vacuum tower may constitute as much as approximately percent of the crude. Residues having the properties set forth above may be visbroken at unexpectedly severe conditions without the formation of excessive coke, as described in our United States Letters Patent No. 2,762,754.

The residue from the vacuum tower is heated in the coil of visbreaking furnace 36 to temperatures in the range of 900 to l000 F., preferably 920 F. to 980 F., to subject the residue to a short-period, high-severity visbreaking process. Pressure has relatively little effect on the severityl of the visbreaking, and may range from 50 to 1000 p. s. i. gauge. The time of cracking is indicated by a coil volume of approximately-0-020 to 0.035 cubic foot above 750 F. per barrel of throughput per day. The severity of cracking at these conditions is such that the yield of 400 F. end point gasoline is in the range of 8 to 20 percent. The severe cracking conditions employed in visbreaking furnace 36 will result in the formation of excessive amounts of coke if charge stocks employed in the vconventional visbreaking operations are subjected to them. n

The cracked products from the furnace 36 are quenched with cycle oil to a temperature below that at which cracking occurs and are delivered through line 38 to an atmospheric distillation tower 40. A suitable stock for quenching is the cycle stock recovered in the manner hereinafter described and introduced into line 3S through line 41. Gas 'and gasoline are withdrawn from the top of the tower 40 through lineV 43, and a bottom stream is taken from the tower through line 42. The bottom stream is heated in a heater '44, then delivered from the outlet ofthe heater through line 46 to a vacuum tower 48. YVacuum tower 4S is operated at a very high temperature and vacuum to permit a very deep reduction of the visbroken charge to that tower. ln addition, steam is preferably introduced into the charge to the tower 48 through a line 47 to reduce the partial pressure of the hydrocarbons further. A distillation temperature of the order of 1100 F., for example above l075 F., corrected to 760 mm., is employed in the tower 48. A heavy cycle oil is withdrawn overhead from vacuum tower 48 through line 50. Part of the cycle oil may be returned, after cooling in a condenser 52, through line 41 for quenching the visbroken product discharged from the furnace 36. The bottoms from the tower 48, constituting the petroleum pitch of this invention, are withdrawn through line 54.V

The distillation temperature in tower 48 will vary with the desired softening point of thepitch, the crude oil employed as a charge stock, the degree of the rst vacuum reduction and the severity of the visbreaking step. For example, the distillation temperature required in vacuum tower 48 for the production of pitches of dilerent softening points from Kuwait crude which has been visbroken at different temperatures is illustrated in Table I..

TABLE I [Distillaton temperatures required to produce petroleum pitch from visbroken Kuwait crude.]

Distlllation Temperature, F. (Corrected to 760 Mmdg) Visbreaking Temperature, F 900 930 950 1, 095 i, 14s 1, iso

Example 1 A Kuwait crude oil having a gravityv of 31.5 API is reduced by atmospheric distillation and then by vacuum distillation at a temperature of 1030" F., corrected to 760 mm. The bottoms from the vacuum distillation, COnSitutiIlg l17,7% of the crude oil, have a gravity of 5.4 API, a Conradson carbon residue of 22.0, and an SUS viscosity at 210 F. of 16,200. The residue is visbroken at a temperature of 950 F. and pressure of 200 pounds per square inch to produce approximately gasoline. The visbroken products are stripped in an atmospheric distillation and then vacuum distilled at a temperature of 1150 F., corrected to 760 mm., to produce a pitch as a residue, and an overhead catalytic cracking charge stock. The pitch has a specic gravity of 1.196, a softening point, ring and ball ASTM D-36-26, of 415 F., and a Conradson carbon residue of approximately 63. The pitch is practically completely soluble in trichloroethylene, benzene, and carbon disulde.

The deep vacuum reduction following the visbreaking of heavily reduced crudes entirely eliminates the production of No. 6 fuel oil and the necessity of blending cycle oil with bottoms to produce a fuel oil of acceptable viscosity. Moreover, the very deep vacuum reduction of the visbroken bottoms increases the amount of cracking charge stock obtained.

We claim: v

1. A process for the preparation of a petroleum pitch substantially completely soluble in benzene and having a softening point above 350 F. comprising distilling a reduced crude petroleum oil selected from the group consisting of parafinic and mixed base crude oils under a vacuum to produce a residual stock having a Conradson `carbon number of at least 18, an API gravity below 10, and a viscosity, SUS at 210 F., of at least 6000, heating the residual stock to a temperature of 900 to about 1000 F. and quickly thereafter quenching the heated residual stock to visbreak the residual stock in a high severity, short-period visbreaking operation, said visbreaking operation yielding about 15% gasoline and lighter hydrocarbons, flashing low boiling fractions from the visbroken products to leave a visbroken bottoms product, heating the visbroken bottoms, and vacuum distilling the thus heated bottoms at a distillation tempera- -ture above 1075 F., corrected to 760 mm. of mercury absolute pressure, in the presence of steam to form the petroleum pitch as a residual product.

2. A process for the preparation of a petroleum pitch substantially completely soluble in benzene and having a softening point above 350 F. comprising distilling a petroleum crude oil selected from the group consisting of parainic and mixed base crude oils under vacuum to produce a residual stock having a Conradson carbon number of at least 18, an API gravity below 10 and a viscosity, SUS at 210 F., of at least 6000, heating the residual stock to a temperature of 900 to 1000 F. in a coil having a volume above 750 F. of 0.02 to 0.035 cubic foot per barrel of residual stock per day to thermally crack the residual stock to yield about 8 to 20 percent 400 F. end point gasoline, and vacuum distilling the thermally cracked residual stock at a distillation temperature above 1075 F., corrected to 760 mm. of mercury absolute pressure, to form the petroleum pitch as a bottoms product.

3. A process for the preparation of a petroleum pitch substantially completely soluble in benzene and having a softening point above about 350 F. comprising thermally cracking a residual stock consisting essentially of a virgin residue of a petroleum cr-ude oil lselected from the group consisting essentially of paratlinic and mixed base crude oils, said residual stock having a Conradson carbon number of at least 18, an API gravity below 10 and a viscosity, SUS at 210 F. of at least 6000 at a temperature of 900 to 1000 F., in a coil having a volume above 750 F. of 0.02 to 0.035 cubic foot per barrel of residue per day to thermally crack the residue to yield 8 to 20 percent 400 F. end point gasoline, stripping gasoline and lighter fractions from the thermally cracked residual stock in a once-through operation, and vacuum distilling the stripped thermally cracked residue at a distillation temperature above 1075 F., corrected to 760 mm. mercury absolute pressure, to form the petroleum pitch as a bottoms product.

References Cited in the file of this patent UNITED STATES PATENTS 2,305,440 Noel Dec. 15, 1942 2,633,449 Cheney Mar. 31, 1953 2,651,601 Tat et al Sept. 8 1953 2,662,051 Pelzer Dec. 8, 1953 2,663,675 Ewell Dec. 22, 1953 2,696,458 Strickland Dec. 7, 1954 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,847,359 August l2, 1958 Harold Beuther et al.,

It is herebf'; certified that error appears in the-printed specification of the above rvxumbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5 line 44 for "softening point above 3500 FJ' read e softening;y

point above about 350O F u.,

Signed and sealed this 28th day of October 1958.,

( SEAL) Attest:

KARL Ho AXLINE ROBERT C. WATSON Attesting O'icer Commissioner of Patents 

1. A PROCESS FOR THE PREPARTION OF A PETROLUM PITCH SUBSTANTIALLY COMPLETELY SOLUBLE IN BENZENE AND HAVING A SOFTENING POINT ABOVE 350*F. COMPRISING DISTILLING A REDUCED CRUDE PETROLEUM OIL SELECTED FROM THE GROUP CONSISTING OF PARAFFINIC AND MIED BASE CRUDE OILS UNDER A VACUUM TO PRODUCE A RESIDAL STOCK HAVING A CONRADSON CARBON NUMBER OF AT LEAST 18, AN API GRAVITY BELOW 10, AND A VISCOSITY, SUS AT 210*F. OF AT LEAST 6000, HEATING THE RESIDUAL STOCK TO A TEMPEATURE OF 900* TO ABOUT 100*F. AND QUICKLY THEREAFTER QUENCHING THE HEATED RESIDUAL STOCK TO BISBREAK THE REIDUAL STOCK IN A HIGH SEVERITY, SHORT-PERIOD VISBREAKING OPERATION, SAID VISBREAKING OPERATION YEILDING ABOUT 15% GASOLINE AND LIGHTER HYDROCARBONS, FLASHING LOW BOILING FRACTIONS FROM THE VISBROKEN PRODUCTS TO LEAVE A VISBROKEN BOTTOMS PRODUCT, HEATING THE VISBROKEN BOTTOMS, AND VACUUM DISTILLING THE THUS HEATED BOTTOMS AT A DISTILLATION TEMPERATURE ABOVE 1075*F., CORRECTED TO 760 MM. OF MERCURY ABSOLUTE PRESSURE, IN THE PRESENCE OF STEAM TO FORM THE PETROLEUM PITCH AS A RESIDUAL PRODUCT. 